Add API endpoints for un/subscribing from/to a label

Closes #15638

13 files changed, 261 insertions, 77 deletions

diff --git a/CHANGELOG b/CHANGELOG
index efb6dc6f610..aedd9f8ebdf 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -47,6 +47,7 @@ v 8.8.0 (unreleased)
   - Bump ace-rails-ap gem version from 2.0.1 to 4.0.2 which upgrades Ace Editor from 1.1.2 to 1.2.3
   - Total method execution timings are no longer tracked
   - Allow Admins to remove the Login with buttons for OAuth services and still be able to import !4034. (Andrei Gliga)
+  - Add API endpoints for un/subscribing from/to a label. !4051 (Ahmad Sherif)
 
 v 8.7.5
   - Fix relative links in wiki pages. !4050
diff --git a/app/models/concerns/subscribable.rb b/app/models/concerns/subscribable.rb
index d5a881b2445..083257f1005 100644
--- a/app/models/concerns/subscribable.rb
+++ b/app/models/concerns/subscribable.rb
@@ -36,6 +36,12 @@ module Subscribable
       update(subscribed: !subscribed?(user))
   end
 
+  def subscribe(user)
+    subscriptions.
+      find_or_initialize_by(user_id: user.id).
+      update(subscribed: true)
+  end
+
   def unsubscribe(user)
     subscriptions.
       find_or_initialize_by(user_id: user.id).
diff --git a/doc/api/labels.md b/doc/api/labels.md
index 3730c07c5a7..b857d81768e 100644
--- a/doc/api/labels.md
+++ b/doc/api/labels.md
@@ -165,3 +165,73 @@ Example response:
    "description": "Documentation"
 }
 ```
+
+## Subscribe to a label
+
+Subscribes the authenticated user to a label to receive notifications. If the
+operation is successful, status code `201` together with the updated label is
+returned. If the user is already subscribed to the label, the status code `304`
+is returned. If the project or label is not found, status code `404` is
+returned.
+
+```
+POST /projects/:id/labels/:label_id/subscription
+```
+
+| Attribute  | Type              | Required | Description                          |
+| ---------- | ----------------- | -------- | ------------------------------------ |
+| `id`       | integer           | yes      | The ID of a project                  |
+| `label_id` | integer or string | yes      | The ID or title of a project's label |
+
+```bash
+curl -X POST -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/labels/1/subscription
+```
+
+Example response:
+
+```json
+{
+    "name": "Docs",
+    "color": "#cc0033",
+    "description": "",
+    "open_issues_count": 0,
+    "closed_issues_count": 0,
+    "open_merge_requests_count": 0,
+    "subscribed": true
+}
+```
+
+## Unsubscribe from a label
+
+Unsubscribes the authenticated user from a label to not receive notifications
+from it. If the operation is successful, status code `200` together with the
+updated label is returned. If the user is not subscribed to the label, the
+status code `304` is returned. If the project or label is not found, status code
+`404` is returned.
+
+```
+DELETE /projects/:id/labels/:label_id/subscription
+```
+
+| Attribute  | Type              | Required | Description                          |
+| ---------- | ----------------- | -------- | ------------------------------------ |
+| `id`       | integer           | yes      | The ID of a project                  |
+| `label_id` | integer or string | yes      | The ID or title of a project's label |
+
+```bash
+curl -X DELETE -H "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v3/projects/5/labels/1/subscription
+```
+
+Example response:
+
+```json
+{
+    "name": "Docs",
+    "color": "#cc0033",
+    "description": "",
+    "open_issues_count": 0,
+    "closed_issues_count": 0,
+    "open_merge_requests_count": 0,
+    "subscribed": false
+}
+```
diff --git a/lib/api/api.rb b/lib/api/api.rb
index 5fd9c30cb42..360fb41a721 100644
--- a/lib/api/api.rb
+++ b/lib/api/api.rb
@@ -57,5 +57,6 @@ module API
     mount ::API::Variables
     mount ::API::Runners
     mount ::API::Licenses
+    mount ::API::Subscriptions
   end
 end
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 2870a6a40ef..406f5ea9139 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -307,6 +307,10 @@ module API
     class Label < Grape::Entity
       expose :name, :color, :description
       expose :open_issues_count, :closed_issues_count, :open_merge_requests_count
+
+      expose :subscribed do |label, options|
+        label.subscribed?(options[:current_user])
+      end
     end
 
     class Compare < Grape::Entity
diff --git a/lib/api/helpers.rb b/lib/api/helpers.rb
index 40c967453fb..5e638dbe16a 100644
--- a/lib/api/helpers.rb
+++ b/lib/api/helpers.rb
@@ -95,6 +95,17 @@ module API
       end
     end
 
+    def find_project_label(id)
+      label = user_project.labels.find_by_id(id) || user_project.labels.find_by_title(id)
+      label || not_found!('Label')
+    end
+
+    def find_project_issue(id)
+      issue = user_project.issues.find(id)
+      not_found! unless can?(current_user, :read_issue, issue)
+      issue
+    end
+
     def paginate(relation)
       relation.page(params[:page]).per(params[:per_page].to_i).tap do |data|
         add_pagination_headers(data)
diff --git a/lib/api/issues.rb b/lib/api/issues.rb
index 40928749481..f59a4d6c012 100644
--- a/lib/api/issues.rb
+++ b/lib/api/issues.rb
@@ -103,8 +103,7 @@ module API
       # Example Request:
       #   GET /projects/:id/issues/:issue_id
       get ":id/issues/:issue_id" do
-        @issue = user_project.issues.find(params[:issue_id])
-        not_found! unless can?(current_user, :read_issue, @issue)
+        @issue = find_project_issue(params[:issue_id])
         present @issue, with: Entities::Issue, current_user: current_user
       end
 
@@ -234,42 +233,6 @@ module API
         authorize!(:destroy_issue, issue)
         issue.destroy
       end
-
-      # Subscribes to a project issue
-      #
-      # Parameters:
-      #  id (required)       - The ID of a project
-      #  issue_id (required) - The ID of a project issue
-      # Example Request:
-      #   POST /projects/:id/issues/:issue_id/subscription
-      post ':id/issues/:issue_id/subscription' do
-        issue = user_project.issues.find(params[:issue_id])
-
-        if issue.subscribed?(current_user)
-          not_modified!
-        else
-          issue.toggle_subscription(current_user)
-          present issue, with: Entities::Issue, current_user: current_user
-        end
-      end
-
-      # Unsubscribes from a project issue
-      #
-      # Parameters:
-      #  id (required)       - The ID of a project
-      #  issue_id (required) - The ID of a project issue
-      # Example Request:
-      #   DELETE /projects/:id/issues/:issue_id/subscription
-      delete ':id/issues/:issue_id/subscription' do
-        issue = user_project.issues.find(params[:issue_id])
-
-        if issue.subscribed?(current_user)
-          issue.unsubscribe(current_user)
-          present issue, with: Entities::Issue, current_user: current_user
-        else
-          not_modified!
-        end
-      end
     end
   end
 end
diff --git a/lib/api/labels.rb b/lib/api/labels.rb
index 4af6bef0fa7..c806829d69e 100644
--- a/lib/api/labels.rb
+++ b/lib/api/labels.rb
@@ -11,7 +11,7 @@ module API
       # Example Request:
       #   GET /projects/:id/labels
       get ':id/labels' do
-        present user_project.labels, with: Entities::Label
+        present user_project.labels, with: Entities::Label, current_user: current_user
       end
 
       # Creates a new label
@@ -36,7 +36,7 @@ module API
         label = user_project.labels.create(attrs)
 
         if label.valid?
-          present label, with: Entities::Label
+          present label, with: Entities::Label, current_user: current_user
         else
           render_validation_error!(label)
         end
@@ -90,7 +90,7 @@ module API
         attrs[:name] = attrs.delete(:new_name) if attrs.key?(:new_name)
 
         if label.update(attrs)
-          present label, with: Entities::Label
+          present label, with: Entities::Label, current_user: current_user
         else
           render_validation_error!(label)
         end
diff --git a/lib/api/merge_requests.rb b/lib/api/merge_requests.rb
index 7e78609ecb9..4e7de8867b4 100644
--- a/lib/api/merge_requests.rb
+++ b/lib/api/merge_requests.rb
@@ -327,42 +327,6 @@ module API
           issues = ::Kaminari.paginate_array(merge_request.closes_issues(current_user))
           present paginate(issues), with: Entities::Issue, current_user: current_user
         end
-
-        # Subscribes to a merge request
-        #
-        # Parameters:
-        #  id (required)               - The ID of a project
-        #  merge_request_id (required) - The ID of a merge request
-        # Example Request:
-        #   POST /projects/:id/issues/:merge_request_id/subscription
-        post "#{path}/subscription" do
-          merge_request = user_project.merge_requests.find(params[:merge_request_id])
-
-          if merge_request.subscribed?(current_user)
-            not_modified!
-          else
-            merge_request.toggle_subscription(current_user)
-            present merge_request, with: Entities::MergeRequest, current_user: current_user
-          end
-        end
-
-        # Unsubscribes from a merge request
-        #
-        # Parameters:
-        #  id (required)               - The ID of a project
-        #  merge_request_id (required) - The ID of a merge request
-        # Example Request:
-        #   DELETE /projects/:id/merge_requests/:merge_request_id/subscription
-        delete "#{path}/subscription" do
-          merge_request = user_project.merge_requests.find(params[:merge_request_id])
-
-          if merge_request.subscribed?(current_user)
-            merge_request.unsubscribe(current_user)
-            present merge_request, with: Entities::MergeRequest, current_user: current_user
-          else
-            not_modified!
-          end
-        end
       end
     end
   end
diff --git a/lib/api/subscriptions.rb b/lib/api/subscriptions.rb
new file mode 100644
index 00000000000..c49e2a21b82
--- /dev/null
+++ b/lib/api/subscriptions.rb
@@ -0,0 +1,60 @@
+module API
+  class Subscriptions < Grape::API
+    before { authenticate! }
+
+    subscribable_types = {
+      'merge_request' => proc { |id| user_project.merge_requests.find(id) },
+      'merge_requests' => proc { |id| user_project.merge_requests.find(id) },
+      'issues' => proc { |id| find_project_issue(id) },
+      'labels' => proc { |id| find_project_label(id) },
+    }
+
+    resource :projects do
+      subscribable_types.each do |type, finder|
+        type_singularized = type.singularize
+        type_id_str = :"#{type_singularized}_id"
+        entity_class = Entities.const_get(type_singularized.camelcase)
+
+        # Subscribe to a resource
+        #
+        # Parameters:
+        #   id (required) - The ID of a project
+        #   subscribable_id (required) - The ID of a resource
+        # Example Request:
+        #   POST /projects/:id/labels/:subscribable_id/subscription
+        #   POST /projects/:id/issues/:subscribable_id/subscription
+        #   POST /projects/:id/merge_requests/:subscribable_id/subscription
+        post ":id/#{type}/:#{type_id_str}/subscription" do
+          resource = instance_exec(params[type_id_str], &finder)
+
+          if resource.subscribed?(current_user)
+            not_modified!
+          else
+            resource.subscribe(current_user)
+            present resource, with: entity_class, current_user: current_user
+          end
+        end
+
+        # Unsubscribe from a resource
+        #
+        # Parameters:
+        #   id (required) - The ID of a project
+        #   subscribable_id (required) - The ID of a resource
+        # Example Request:
+        #   DELETE /projects/:id/labels/:subscribable_id/subscription
+        #   DELETE /projects/:id/issues/:subscribable_id/subscription
+        #   DELETE /projects/:id/merge_requests/:subscribable_id/subscription
+        delete ":id/#{type}/:#{type_id_str}/subscription" do
+          resource = instance_exec(params[type_id_str], &finder)
+
+          if !resource.subscribed?(current_user)
+            not_modified!
+          else
+            resource.unsubscribe(current_user)
+            present resource, with: entity_class, current_user: current_user
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/models/concerns/subscribable_spec.rb b/spec/models/concerns/subscribable_spec.rb
index e31fdb0bffb..b7fc5a92497 100644
--- a/spec/models/concerns/subscribable_spec.rb
+++ b/spec/models/concerns/subscribable_spec.rb
@@ -44,6 +44,16 @@ describe Subscribable, 'Subscribable' do
     end
   end
 
+  describe '#subscribe' do
+    it 'subscribes the given user' do
+      expect(resource.subscribed?(user)).to be_falsey
+
+      resource.subscribe(user)
+
+      expect(resource.subscribed?(user)).to be_truthy
+    end
+  end
+
   describe '#unsubscribe' do
     it 'unsubscribes the given current user' do
       resource.subscriptions.create(user: user, subscribed: true)
diff --git a/spec/requests/api/issues_spec.rb b/spec/requests/api/issues_spec.rb
index 9dd43f4fab3..37ab9cc8cfe 100644
--- a/spec/requests/api/issues_spec.rb
+++ b/spec/requests/api/issues_spec.rb
@@ -623,6 +623,12 @@ describe API::API, api: true  do
 
       expect(response.status).to eq(404)
     end
+
+    it 'returns 404 if the issue is confidential' do
+      post api("/projects/#{project.id}/issues/#{confidential_issue.id}/subscription", non_member)
+
+      expect(response.status).to eq(404)
+    end
   end
 
   describe 'DELETE :id/issues/:issue_id/subscription' do
@@ -644,5 +650,11 @@ describe API::API, api: true  do
 
       expect(response.status).to eq(404)
     end
+
+    it 'returns 404 if the issue is confidential' do
+      delete api("/projects/#{project.id}/issues/#{confidential_issue.id}/subscription", non_member)
+
+      expect(response.status).to eq(404)
+    end
   end
 end
diff --git a/spec/requests/api/labels_spec.rb b/spec/requests/api/labels_spec.rb
index 6943ff9d26c..b2c7f8d9acb 100644
--- a/spec/requests/api/labels_spec.rb
+++ b/spec/requests/api/labels_spec.rb
@@ -190,4 +190,86 @@ describe API::API, api: true  do
       expect(json_response['message']['color']).to eq(['must be a valid color code'])
     end
   end
+
+  describe "POST /projects/:id/labels/:label_id/subscription" do
+    context "when label_id is a label title" do
+      it "should subscribe to the label" do
+        post api("/projects/#{project.id}/labels/#{label1.title}/subscription", user)
+
+        expect(response.status).to eq(201)
+        expect(json_response["name"]).to eq(label1.title)
+        expect(json_response["subscribed"]).to be_truthy
+      end
+    end
+
+    context "when label_id is a label ID" do
+      it "should subscribe to the label" do
+        post api("/projects/#{project.id}/labels/#{label1.id}/subscription", user)
+
+        expect(response.status).to eq(201)
+        expect(json_response["name"]).to eq(label1.title)
+        expect(json_response["subscribed"]).to be_truthy
+      end
+    end
+
+    context "when user is already subscribed to label" do
+      before { label1.subscribe(user) }
+
+      it "should return 304" do
+        post api("/projects/#{project.id}/labels/#{label1.id}/subscription", user)
+
+        expect(response.status).to eq(304)
+      end
+    end
+
+    context "when label ID is not found" do
+      it "should a return 404 error" do
+        post api("/projects/#{project.id}/labels/1234/subscription", user)
+
+        expect(response.status).to eq(404)
+      end
+    end
+  end
+
+  describe "DELETE /projects/:id/labels/:label_id/subscription" do
+    before { label1.subscribe(user) }
+
+    context "when label_id is a label title" do
+      it "should unsubscribe from the label" do
+        delete api("/projects/#{project.id}/labels/#{label1.title}/subscription", user)
+
+        expect(response.status).to eq(200)
+        expect(json_response["name"]).to eq(label1.title)
+        expect(json_response["subscribed"]).to be_falsey
+      end
+    end
+
+    context "when label_id is a label ID" do
+      it "should unsubscribe from the label" do
+        delete api("/projects/#{project.id}/labels/#{label1.id}/subscription", user)
+
+        expect(response.status).to eq(200)
+        expect(json_response["name"]).to eq(label1.title)
+        expect(json_response["subscribed"]).to be_falsey
+      end
+    end
+
+    context "when user is already unsubscribed from label" do
+      before { label1.unsubscribe(user) }
+
+      it "should return 304" do
+        delete api("/projects/#{project.id}/labels/#{label1.id}/subscription", user)
+
+        expect(response.status).to eq(304)
+      end
+    end
+
+    context "when label ID is not found" do
+      it "should a return 404 error" do
+        delete api("/projects/#{project.id}/labels/1234/subscription", user)
+
+        expect(response.status).to eq(404)
+      end
+    end
+  end
 end